102 The Phenomena of Morphogenesis 



than does the epicotyledonary bud itself and believes that this is owing 

 to the removal by these leaves of some food material necessary for bud 



growth. 



Other structures may be inhibited. If root nodules and root tips are re- 

 moved from roots of red clover inoculated with an effective strain of 

 nodule bacteria, the number of nodules subsequently formed will be in- 

 creased (Nutman, 1952). This is thought to be owing to the removal of 

 inhibitory activity centered in the meristems of nodules and root. 



Inhibition by terminal buds has various practical implications. Reed 

 ( 1921 ) found that heavily pruned young pear trees have a greater growth 

 of new shoots than do unpruned or lightly pruned ones and suggests that 

 this results from the removal from them of much growth-inhibiting sub- 

 stance present in the buds near the tips of the branches. 



Correlations of Position. Many parts of the plant can be shown to have 

 the capacity for much more extensive growth than they normally display. 

 If a leaf is removed and treated as a cutting, it will frequently grow to a 

 greater size and live much longer than if it had remained a part of the 

 plant (Mer, 1886; Riehm, 1905; Winkler, 1907; and others). Single cells, 

 under suitable conditions of isolation and stimulation, will sometimes de- 

 velop into whole plants. All parts of the plant tend thus to be totipotent. 

 Why these potentialities are not realized when the part is a member of 

 an organic whole is a problem. Not only is each part of this whole limited 

 in its growth, but the particular way in which it develops depends on 

 where it is. Driesch's famous dictum emphasizes the fact that an or- 

 ganism is an organic pattern in which every part develops in a specific 

 relation to the rest. The correlations that these parts display with one an- 

 other are simply manifestations of the control that this pattern exercises 

 in development. 



Experimental change of the position of a part in this pattern often 

 effects marked alteration. Ward and Wetmore (1954) partially released 

 young fern embryos from their contact with the prothallus and found 

 their growth to be slower and somewhat abnormal. Wetmore asks the sig- 

 nificant question as to why a spore and an egg should grow so differently. 

 Each is a haploid cell and they presumably are identical genetically, but 

 the surroundings under which they develop are very different. He sug- 

 gests that perhaps the difference between sporophyte and gametophyte 

 in ferns may be the result of this positional correlation. 



Mason (1922) reports that the terminal bud from a cotton shoot that 

 has stopped growing will grow vigorously if it is budded on a young plant. 

 A flower bud inserted on a vegetative shoot where it would not normally 

 occur often changes in its development and may produce a flower cluster 

 which is gigantic or otherwise abnormal. 



The operation of such a constantly regulated balance among activities 



